An output circuit is a well known type of circuit that is implemented in an integrated circuit for providing an output signal. Advanced integrated circuits may include a plurality of output circuits providing different types of signaling, such as single-ended or differential signaling. Differential signaling is a method of transmitting electrical signals by means of two complementary signals sent on two separate wires such as traces of a printed circuit board (PCB). Differential signals are typically coupled in differential pairs usually found on a PCB, in cables (twisted-pair cables, ribbon cables), and in connectors. Differential pairs are usually used to couple high speed signals (e.g., digital serial interface signals) or high frequency analog signals (e.g., video signals). Advantages of utilizing differential signaling may include tolerance to ground bounce or offsets, low-voltage signaling, minimized cross-talk, and increased resistance to electromagnetic interference. The complementary or differential signals described above are usually referenced to a ground potential or common-mode voltage (Vcm).
As noted above, examples of output circuits may include differential driver circuits providing complementary signals referenced to a common-mode voltage. The Vcm is a voltage having a positive or a negative value with reference to a ground potential, depending on the signaling design protocol. For example, Low-voltage differential signaling (LVDS) is a differential signaling system that can run at very high speeds over conductive wires or traces of a PCB. The LVDS standard, for example, may support differential output signals having voltage amplitude in the range of 250-450 mV and a voltage offset or Vcm in the range of 1.125-1.375 V.
There are other differential signaling protocols, for example, current-mode logic (CML), low-voltage positive/pseudo emitter-coupled logic (LVPECL). In general, integrated circuits may include various types of output circuits. The various output circuits may provide interfaces to support single ended signaling and/or differential signaling.